Book Review: Devices For Electronic Systems, Rechargeable Batteries And Supercapacitors

A book authored by Nihal Kularatna and faculty members of the School of Engineering, The University of Waikato (Hamilton, New Zealand) describes Energy Storage Devices and their applications.

The book is organized as follows:

1. Energy storage devices (ESDs) — a general overview

The first chapter discuses Work, power, and energy and the equations associated with this these fundamentals. Other subjects include the impact of the open circuit voltage and internal resistance of an energy source, energy wasted inside a source and its heating effect, and time delays in delivering or transferring energy.

Energy storage requirements come in two basic forms: short-term storage where components in powered electrical circuits store energy in electrostatic or electromagnetic form and longer term storage for a redundant energy source.

Many types of rechargeable chemistry are used in electronic systems. Common rechargeable chemistries are based on variations of lead acid, nickel-based and lithium-based systems mainly, while limited zinc-based systems and rechargeable alkaline batteries are also available. The choice of a particular battery technology is limited by size, weight, cycle life, operating temperature range, and cost.

This chapter also describes battery terminology and fundamentals.

3. Dynamics, models, and management of rechargeable batteries

In a rechargeable battery pack, state of charge (SOC), state of health (SOH), and end of life (EOL) become important overall quality parameters of an installed pack. In determining optimal management criteria for the longest lifetime and the longest run time of the battery pack, circuit designers have to clearly understand battery dynamics and use optimal battery models to design the correct battery management system (BMS).

This chapter provides some fundamentals of battery dynamics, different types of modeling to achieve usable and practical equivalent circuits, and an overview of management systems for different applications. In this chapter, electrochemistry based modeling approaches are highlighted to better understand the behavior of popular rechargeable chemistries, without going into the mathematics.

This chapter describes a capacitor as a device with two electrodes (plates) that stores electrical charge and releases the charge when required by the circuit. When a DC voltage is applied to the capacitor electrodes, an electrical charge builds up on the capacitor plates with electrons producing a positive charge on one plate and an equal and opposite negative charge on the other plate. In a fully-charged capacitor , current flow continues until the potential difference between the two electrodes becomes equal to the supply voltage.

There are many variations in very high capacitance, low voltage devices variously referred to as supercapacitors, ultracapacitors, or electrochemical double-layer capacitors (EDLCs). They store charge in an electrical double layer at the interface between a high surface area electrode and an electrolyte. Current commercial devices are relatively low voltage single-cell devices with DC voltage ratings up to about 16 V or series-connected modules with voltage ratings up to and over 100 V DC. Supercapacitors are capable of providing short-duration power bursts, and have life cycles of half a million to several millions.

6. Supercapacitor as a lossless dropper in DC-DC converters

Co-Author Kosala Gunawardane

This chapter describes how a supercapacitor can be used as a lossless dropper that can improve end-to-end efficiency (ETEE) of a linear regulator based on low dropout regulators (LDOs).

7. Supercapacitors for surge absorption

This chapter describes a supercapacitor’s ability to absorb high-voltage (HV) transient surges. By controlling the duration of occurrence of a HV source to a “short-enough” period, final voltage across the terminals of the capacitor will be kept within safe limits. Therefore, a very large value capacitor, such as a supercapacitor in a circuit loop of finite series resistance, can safely absorb energy from a short-duration HV (transient) source.

8. Supercapacitors in a rapid heat transfer application

State-of-the-art supercapacitors (SCs) come in all sizes from fractional farads to over 5000 F in single-cell. For smaller value devices their equivalent series resistance (ESR) values range from about 25 mW to 100 mW. The larger capacitance devices from about 300 to 5000 F have much lower ESR values such as 0.3 mW to about 5 mW.

Applyjng this fact to a typical battery and a SC to estimate the maximum possible output power, we could see that the internal resistance device is the primary determining factor. In this chapter we discuss the case where we could use a bank of SCs to fast-heat water flowing in domestic water systems and to minimize the waste of treated water due to the stored cold water in domestic pipes between the central water heater and the individual faucet.

Appendix A: capacitors and AC line filtering

Co-author: Nicoloy Gurusinghe

One of the most common applications of capacitors is to apply them as AC line frequency filters in AC to DC converters. Usually a half-wave or a full-wave bridge rectifier is used together with an electrolytic capacitor of a sufficient value, to smooth out the rectified waveform so that the output is an average DC voltage with a limited peak to peak 50/60 or 100/120 Hz ripple waveform superimposed on the DC. This discussion compares the performance of electrolytic capacitors and supercapacitors in AC-DC converters to show why the present-day supercapacitors are not suitable for the specific application.